Titanium biological activity

Biomedical materials include ceramics such as the biologically active hydroxylapatite and tricalcium phosphate, and high-strength metals such as titanium alloys.These materials are not produced by CVD as this time, except on an experimental basis. CVD, however, is the major process used in the production of another very important biomedical material, i.e., isotropic... 

Asymmetric hydrogenation of nitrones in an iridium catalyst system, prepared from [IrCl(cod)]2, (S)-BINAP, NBu 4 BH4, gives with high enantioselectivity the corresponding A-hydroxylamines which are important biologically active compounds and precursors of amines (480). Further reduction of hydroxylamines to secondary amines or imines can be realized upon treatment with Fe/AcOH (479), or anhydrous titanium trichloride in tetrahydrofuran (THF) at room temperature (481). 

Thus, with proper choice of chiral template and aldehyde, all four possible syn- and anti-aldol products can be prepared with predictable stereochemistry. Both boron and titanium enolate methodologies have been successfully applied to the stereoselective syntheses of several biologically active compounds66-69 and natural product synthons.61-70-71... 

In term of diversity-oriented strategies, multicomponent reactions (MCR) represent an attractive and rapid access to libraries of macrocycles inspired by biologically active natural products. Combined with Passerini and Ugi reactions, M-RCM has already shown promising synthetic potential, as illustrated by the pioneering work of Domling and coworkers [46]. Condensation of isocyanide 69 with carboxylic acid 70 in the presence of paraformaldehyde leads to bis-olefin 71, which is subsequently submitted to RCM in the presence of G1 and titanium isopropoxide to give the 22-membered macrocycle 72 (Scheme 2.27). 

Breitenbucher and Hui (104) have recently reported the SP synthesis of a medium-large discrete library L3 of 8448 benzopyrans using the reductive amination cocktail formed from titanium isopropoxide and sodium triacetoxyborohydride, known in solution but whose applications to SP were rare and limited to single experiments (105, 106). The benzopyran scaffold is present in a number of biologically active compounds (107-110), and this library was tested in several biological assays (111). 

Chiral sulfoxides have become an important class of compounds as cbiral auxiliaries in asymmetric syntheses, as metabolites of sulfide-containing drugs, and also as biologically active ingredients themselves. Kagan s modification of the titanium-tartrate reagent by adding one mole equivalent of water has paved the way for a practical synthesis of chiral sulfoxides [88]. 

A series of titanium chelate complexes with biologically active monofunctional bidentate semicarbazones having 0,N donors have been prepared by reacting Cp2TiCl2 with the appropriate ligand in 1 1 and 1 2 stoichiometries. The ligands were prepared by condensing heterocyclic ketones and semicarbazide hydrochlorides in presence of NaOAc.1583... 

The asymmetric oxidation of sulfides represents a straightforward access to chiral sulfoxides that are useful compounds for asymmetric synthesis as chiral auxiliaries and also for the synthesis of biologically active molecules. Among the different methods to perform these reactions, titanium-mediated thioether oxidation is one of the most attractive. Indeed, Kagan ° and Modena independently showed that the use of chiral titanium complexes derived from Sharpless reagent allows the asymmetric oxidation of prochiral sulfides (Scheme 7.6). 

Ternary and quaternary a-hydroxy-phosphonates, an important class of biologically active compounds, are commonly obtained by addition of dialkylphosphites onto aldehydes or ketones [30]. Well-defined mono- or bimetallic complexes of rare-earth metals, titanium, or aluminum have emerged over the past two decades as effective catalysts for this so-called hydrophosphonylation of aldehydes [31] and, with more difficulty, that of ketones [31c,d, 32], which are far less reactive because of their lower electrophilicity. In some cases, good enantioselectivities could be achieved thanks to the use of chiral metal-based precatalysts [31, 32], Despite their several similarities with rare-earth elements, we were surprised to see that discrete complexes of the large Ae metals had never been utilized to catalyze hydrophosphonylation reactions. 

Also a titanium dioxide mesoporous film on indium tin oxide (ITO) was decorated with gold nanoparticles, and hemoglobin was immobilized on its surface in such a way to retain the secondary structure and biological activity. The Fe -PPIX redox couple was found at -0.29 V and exhibited electrocatalytic response for hydrogen peroxide in the 5.0-1000 pM range and limit of detection of 0.6 pM, with good stability and reproducibility [171]. 

Cossy J, BouzBouz S, Pradaux F, Willis C, Belosta V. Chiral titanium complexes. Synthesis of optically active unsaturated alcohols, diols, pol)fpropionates and their use in the synthesis of biologically active compounds. Synlett 2002 1595-1606. 

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